1. The Field of the Invention
This invention relates to pressure relief mechanisms for operation in ultra-pure environments and, more particularly, to novel systems and methods for providing burst disks in metal-free, ultra-pure, environments subjected to liquids at elevated temperatures, with respect to ambient.
2. Background Art
Pressure relief is a critical function in systems managing, transporting, or relying upon fluids. Fluids include gases and liquids. Many industrial processes rely on hot liquids, heated to temperatures that may damage, weaken, leach, or otherwise interact with metals, polymers, and other common materials.
One industry that has suffered with the limited technology of pressure relief devices is the semiconductor processing industry. For example, hot, de-ionized water is used in numerous processes. Impurities are measured in parts per billion. Some materials may be hot acids used in etching and cleaning processes. Transportation, holding, heating, and other procedures for managing ultra-pure water, acids, and the like, are problematic in several ways.
For example, burst disks have traditionally been made of metal. Regardless of the "stainlessness" of a metal, the purity requirements are not met by any known metals. Polymers may similarly leach, react, degrade, or otherwise contaminate liquids. Moreover, polymers are typically not dimensionally stable. Polymers creep, stretch, yield, and otherwise become unreliable. As burst materials, polymers (plastics, elastomers) respond to load, pressure, time, and chemical environment, destroying any hope of reliability and repeatability.
Polymer-coated metals have been proposed. No apparatus is perfect. Pinholes may be created by creep or yielding of polymers. Pinholes may be formed during manufacturing. Thin layers do not achieve perfect coverage. Detection of flaws ranges from extremely difficult to impossible. Failures can be catastrophic.
Contaminants exceeding allowable limits may destroy a batch of a product. Physical destruction is not required. Rendering a wafer unusable due to contaminant reactions with a surface can waste product output.
What is needed is a pressure relief mechanism that is absolutely clean before and after release. All materials that may potentially contact contained fluids, even in the event of failures, should be pure and non-reactive. Materials should tolerate elevated temperatures in the range of 100 degrees Fahrenheit to 200 degrees Fahrenheit. In some acids, temperatures may range from 100 degrees Celsius to 200 degrees Celsius. These temperatures represent pressurized systems operating above the ambient boiling temperature of water. Saturation pressures are commensurate with the thermodynamics of the contained fluid.
Thus, stability over a broad range of temperatures, reliability in service, long life under exposure to extreme of temperatures, pressure, and reactive agents, and the like must all be tolerated. Repeatability of designs, and reliable repeatability over the life time of an installed pressure-relief apparatus are very desirable. Currently, complex valve mechanisms are the most reliable devices used. Polymeric burst disks are not repeatable in service. Metals are reactive. Polymer-coated metals still fail to maintain purity reliably.
What is needed is a reliable burst disk mounted in a fixture that maintains purity, providing dimensional stability and long term repeatability at elevated temperatures, pressures, and reactivities.